1. Field of the Invention
This invention relates generally to improvements in highway construction machinery, and more particularly, but not by way of limitation, to flywheels incorporated in a cutting tool drive train of such machinery.
2. Description of the Prior Art
In the art of highway construction, various types of machines are used to cut earth and other materials for various purposes; for example, the preparation of a road bed. An example of such a machine, used to remove the upper surface of a previously paved roadway, is described in the co-pending application of Herbert Edward Jakob and Richard A. Silbernagel entitled "Method and Apparatus for Planing a Paved Roadway", Ser. No. 672,326, and assigned to the assignee of the present invention.
Machines designed to provide a cutting function often employ a rotationally driven cutting tool driven by a hydraulic motor which, in turn, is powered by pressurized hydraulic fluid provided by a hydraulic pump. For example, in the machine described in the above referenced application, the cutting tool is a drum having a plurality of cutters positioned on a spiral flight wrapped around the drum. The drum is rotated as the machine is moved along a roadway so that the cutters are driven into the roadway to remove a layer of the roadway. The hydraulic motor used to rotate the drum operates at a relative high rate of rotation and is coupled to the drum through a gear reduction box to reduce the speed with which the drum rotates. A chain drive is used to connect the gear reduction box to the drum.
A problem, which is especially acute when the cutting tool is driven by means of a hydraulic drive system incorporating a swash plate type pump, occurs with machines which carry out a cutting function. As the cutting tool is driven into a paved roadway or earth, mechanical shocks are generated in the cutting tool and fed back into the drive system. These shocks can reduce the lifetime of the drive system. The problem is especially acute when the drive system includes a swash plate type pump because such pumps utilize the pressure in the return line from a hydraulic motor driven by the pump to maintain contact between working parts of the pump. It has been found by experimentation that mechanical shocks generated in the cutting tool can reduce the return line pressure to a value insufficient to maintain the required contact. The result is an internal battering of the pump caused by successive disengagement and engagement of internal parts of the pump.
It is known that a flywheel in the drive train of a cutting tool will reduce mechanical shock fed back to the drive system of the cutting tool. A trencher incorporating a flywheel in the cutting tool drive train has been produced using a gear box having an integral flywheel and produced by Power Engineering and Manufacturing, Ltd. of 724 Sycamore Street, Waterloo, Iowa, 50703 and the use of a flywheel in a hydraulically driven conveyor in an earth scraper is disclosed in U.S. Pat. No. 3,208,165 issued Sept. 28, 1965 to C. M. Johnson and J. E. Lowder.
However, the use of a flywheel for shock reduction can introduce a second problem. If the cutting tool is suddenly stopped, the drive train transmits forces from the cutting tool to the flywheel to exert a torque on the flywheel tending to halt the flywheel in the same period of time that the cutting tool is halted. If this time is short and if the angular momentum of the flywheel is large, the magnitude of forces sufficient to exert the required torque can also be sufficient to shear teeth from gears or to break a chain in a drive train which transmits these forces. In a construction machine such as the roadway planer described in the aforementioned patent application, Ser. No. 672,326, the angular momentum of the flywheel must be large if the flywheel is to effectively isolate the drive system for the cutting tool from mechanical shock generated by driving cutting tools into a concrete or asphalt surface.
Rapid stoppages are not uncommon when the construction machine is a roadway planer such as that described in the above-referenced patent application. Such machines are used on paved roadways and it is not always possible for the operator of the machine to avoid driving the cutting tool across a manhole or the like. Moreover, such machines must have considerable weight to force cutters into a pavement so that the machine will have little tendency to climb away from the exceptional load presented by such obstacles as a manhole. Rather, it is likely that the cutting tool will be brought rapidly to a halt.